1. Field of the Invention
The present invention relates to a system for a broadcast service in a passive optical network (PON) system, and more particularly, to a time division multiple access (TDMA) PON optical line terminal (OLT) system enabling a simultaneous broadcast and communications service through a single optical cable.
2. Description of the Related Art
Network businesses have invested heavily in triple play services (TPSs) capable of processing broadcasts, sound, and data in one network.
Many more downstream bandwidths are required toward an optical network terminal (ONT) in an OLT to provide a broadcast service such as Internet protocol television (IPTV) to subscribers using a fiber to the home (FTTH) network.
Downstream traffic is heavier than upstream traffic in an ultrahigh speed Internet network. Thus, if a broadcast service is additionally provided, a ratio of the downstream traffic to the upstream traffic is seriously asymmetric.
However, in a gigabit PON (GPON) system recommended in ITU-T G.984.1.about.2, a ratio of downstream traffic to upstream traffic may be within a range between 1:1 and 1:4. In a case of an Ethernet PON (EPON) system standardized in IEEE 802.3ah, a ratio of downstream traffic to upstream traffic is 1:1.
Therefore, in a current TDMA PON system and a current network structure, network efficiency is deteriorated due to expected serious asymmetry of upstream and downstream speeds. This increases cost of OLT equipment.
A multicasting method used in a TDMA-PON to solve this problem may delay a change of a channel and thus cause inconvenience to a user. Also, a broadcasting method using additional wavelength division multiplexing requires a high-priced optical transceiver and a high-priced optical amplifier to provide only a broadcast signal.